The present invention relates to communications in, for example, wireless local area networks, mobile/cellular and other wireless networks.
In multi-hop wireless networks, such as mobile ad hoc networks, nodes store and forward data frames for each other so the frames can be forwarded to distant destinations that are not within direct wireless communication reach of data sources. Such a forwarding mechanism has not been adopted into wireless local area networks (WLANs). In WLANs, access points are attached to a distribution system (DS), typically a wired local area network (LAN), and stations and access points are within direct communication range of each other. In other words, WLAN architecture extends the boundaries of a distribution system by only one wireless hop. Both station to outside-of-cell (via DS) and outside-of-cell to station types of traffic are directly between the access point and the station. Station to station traffic is transmitted from source station directly to access point then access point directly to destination station. Thus, one might think that there is no need for client stations to forward frames for intra-cell data forwarding, meaning the forwarding of frames to an access point by other client stations of the same cell, i.e., communicating with the same access point.
However, a closer examination of real world WLAN deployments leads to a different conclusion. In these systems, access points are typically at an advantage in terms of radio transmission and reception, as compared to the client stations they serve. Access points are supplied with commercial electrical power while client stations usually are battery-operated. Access points may have additional signal amplification modules and large antenna structures, while client stations usually only have the dimension-limited internal hardware of their wireless network interface cards. The asymmetry between the capabilities of access points and client stations is even more pronounced in special systems such as sensor networks or other networks where the client stations (e.g., sensor nodes) have very limited communication resources.
Because the design of WLAN protocols presumes that client stations and their access points are within range of each other, the coverage area of each cell, i.e., area served by a particular access point, is limited by client station communication capabilities. For example, a distant station, even if within an access point's transmission range, may not be served by the access point because the station's own transmissions are not strong enough to reach the access point. The superior communication capabilities of the access points thus can not be fully taken advantage of.
Intra-cell upstream data forwarding can help. With intra-cell upstream data forwarding, client stations forward other client stations' communications to the access point. This approach has the advantage of increasing the effective service area of each access point because now coverage is limited by the transmission range of the access point and no longer that of the client stations. This effectively reduces the number of access points required for covering an area and thus reduces deployment costs.
In addition, intra-cell upstream forwarding also helps client stations to conserve their valuable battery power. Each shorter transmission consumes less transmission power at each station, and the total energy consumption of multiple transmissions across a certain distance is still typically less than what is consumed by a single long-range transmission over the same distance.
Despite its many advantages, the intra-cell upstream forwarding mechanism has not been widely used. A significant reason relates to the complexity of setting up and maintaining the forwarding paths. Client stations need to exchange control messages to learn about each others' positions relative to the access point and to compute how other stations can be used as forwarding nodes. In mobile scenarios where client station positions change, thereby causing forwarding topology change, more frequent control message exchanges are required to ensure the correctness of forwarding path computation. These known approaches are expensive in terms of communication, computation, and storage overhead, as well as in design and implementation complexity.